Usually, a wireless communication system uses an electromagnetic wave and a fixed/mobile wireless communication terminal (for example, a mobile wireless phone or a laptop contained a wireless communication card, and etc., can be called terminals for short) for communicating. Generally, terminals are located within the radio coverage area of a system, and the electromagnetic wave frequencies assigned to such terminals are divided into multiple carrier frequencies as radio communication channels. The wireless communication system provides radio coverage within a certain geographic area using a designated radio channel through a Base Station (BS for short), and the geographic area is called a Cell. Usually, the base station is located at the center of the cell.
The coverage area of a wireless network can be affected by various factors. For example, high buildings may shield the radio signals of the base station, which leads to a severe attenuation of signals within a certain area, and signals at the edge of the cell will also be attenuated, thereby increasing the probability of the reception error of the terminal. The capacity requirement of the wireless communication system can also be affected by many factors, for example: when the number of users increases sharply or the amount of traffic increases sharply, the system capacity is required to be expanded; while in a rural area, the capacity of one base station usually cannot be fully used in the coverage area, and then the coverage range of the system needs to be expanded to use the redundant system capacity.
To expand the system coverage range or the system capacity, one or more Relay Stations (RS for short) can be set between a base station supporting multi-hop relay and a terminal (hereinafter the wireless communication system including the relay station is called a system for short). The relay station can be used to relay the signal from the base station to the terminal (downlink) or from the terminal to the base station (uplink). After using the relay station, the signal transmission quality of a communication link can be improved effectively and thus the object of expanding the system coverage range or increasing the system capacity can be achieved.
The communication path that a terminal accesses to a base station via one or more hops of relay station is called a relay path. The relay station directly connected with the terminal is called an access relay station. The communication link between the access relay station and the terminal is called an access link. On the relay path, the access relay station can communicate with the base station through other relay stations. On the relay path, the communication links between the relay stations and between the relay stations and the base station are called relay links. The relay station can be fixed, roaming or mobile.
As described above, current relay-based wireless communication methods are mostly pure uplink transmission or downlink transmission, that is, data sent by a terminal must be first uplink transmitted to the base station which then downlink transmits the data to a target terminal. In the case of a relative small distance between a sending end and a transmitting end, the above processing methods obviously prolong the data transmission path, and thus data transmission delay is increased correspondingly.
However, no technical solution that can solve this problem has been proposed so far.